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Birkin serenaded the exiting Lionsgate Motion Picture Group co-chairman at the Hotel du Cap: "It was his first job, and he was her driver. That's why she performed tonight."

Picture a group of Hollywood’s heaviest hitters watching transfixed as a singer performs at Cannes. Such was the case as British-French icon of the ’70s and ’80s Jane Birkin serenaded Patrick Wachsberger at an “au revoir” party May 11 at the Hotel du Cap held in honor of the exiting Lionsgate Motion Picture Group co-chairman.

In fact, Birkin (who served as the inspiration for the eponymous Hermes bag) told the crowd that it’s the first time she ever got up and sang at a party. “Patrick and Jane have a backstory,” Lionsgate CEO Jon Feltheimer told THR at the gala. “It was his first job, and he was her driver. That’s why she performed tonight.”

Making the moment even sweeter, Wachsberger, 66, hadn’t seen Birkin, mother of actress Charlotte Gainsbourg, in 42 years. The two first met in 1970 when Wachsberger was 19 years old on the set of Cannabis, a movie that Birkin and Serge Gainsbourg were filming around the time their 13-year relationship ignited (technically, Wachsberger was 2nd assistant director).

Wachsberger and Birkin also worked together in 1973 on Seven Dead in the Cat’s Eye. “While I may take a few moments to enjoy the Mediterranean this summer, this is not a retirement party at all,” Wachsberger told the crowd. “There is much I intend to do between Lionsgate and pearly gates.”

Among those craning their necks for a better view of Birkin’s "As Time Goes By" were Christopher Nolan, Jim Gianopulos, Simon Kinberg and Doug Liman.

A version of this story first appeared in the May 16 issue of The Hollywood Reporter magazine. To receive the magazine, click here to subscribe.